The invention relates to new, heavily oil extended, peroxide curable unsaturated ethylene copolymer compositions that, when cured, result in an elastomer having excellent physical properties equivalent to those of peroxide cured compositions which have no oil.
Peroxide curable ethylene/higher .alpha.-olefin/non-conjugated diene copolymers (EODM) are useful for wire and cable jackets, radiator hose, electrical connectors, and in ozone resistant blends with natural rubber, SBR, and other highly unsaturated elastomers. Peroxide cured EODM elastomers are preferred for certain uses because they show better heat stability than sulfur cured EODM's; that is, their physical properties do not change significantly when they are exposed to high temperatures during extended use.
It is economically desirable and often advantageous from a processing standpoint to incorporate substantial amounts, e.g., as much as 100 phr or more, of extending oils in the ethylene copolymer composition. Unfortunately, high oil dilution of these unsaturated ethylene copolymers creates problems when a peroxide cure is contemplated, as noted by Baldwin and ver Strate [Rubber Chem. & Tech. 45 No. 3, p. 806 (April 1972)] because the peroxide can react with the oil as well as with the copolymer; therefore, in effect, the oil lowers the effectiveness of the peroxide, decreases the rate of cure, and lowers the state of cure attained. An EODM composition that contains large quantities of extending oil and, in spite of the presence of the oil, is curable by employing conventional amounts of peroxides to products having good physical properties has been a goal of the industry.